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Review and Measurements of Neurochrome HP-1 High-Performance Amp

bozoc

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Even volume control chips such as Cirrus 3310 or the BB PGA 2310 will wiped the floor on any mechanical volume pots. That include all Alps, Allen Bradley, TKD and the like. Whether they’d be carbon or plastic film, they will all degrade from the initial physical turn regardless of what people claim.
Even though they do not have any moving parts they do not really "wipe the floor on any mechanical volume pots", far from it. Pots have a lifetime and people have anecdotally reported quality issues with 9mm alps. RK27 looks nice and sturdy, TKD are somewhat pricey but have good tracking, I have Bourns 9mm and RK27 in my amps/preamps and never had a problem.

Personally, humble pot is good enough for me as other solutions have a lot more downsides IMO, for example resistors networks require a lot of relays(more mechanical moving parts and relay switching noise). Maybe there could be different footprints on PCB so people can pick their poison RK27, TKD, boruns etc...
 
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That could be. However, how do you get an encoder to "feel" right? How do you move users past the experience of the "infinite turns" volume knob? Life as we know it will never be the same. :)
As a non-EE, I'll risk Dunning-Kruger here... How about using a motorized pot to set a DC reference which controls the real attenuator? Seems you could ignore the pot's audio qualities, allowing you to select a part based on feel. In addition, the knob could offer the traditional 7-5 o'clock range and remember - & display! - its setting thru a power cycle.
 

restorer-john

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How about using a motorized pot to set a DC reference which controls the real attenuator?
More unnecessary Rube-Goldberging.

I have some 80s/90s examples that would blow your mind with volume controls, input selectors and other analog style 'modernisations'.

Sansui incorporating a microprocessor 'auto-search' system on an analogue tuner (T-7) that through a complicated worm/reduction drive and clutch would zoom the tuner pointer across the dial and stop on a station using up/down buttons.

Sony wanting to get in on the flat panel/no volume knob train by using an internal 270 degree pot driven by logic and a motor drive, also moving a plastic bar-graph that was backlit from behind to look like a volume 'meter'.

Sony's TOTL TAE-80es preamplifier with a ridiculously unreliable motorised internal input selector that is another nightmare to repair.

Yamaha motor driving their rotary input selectors via remote control, replete with a little indicator LED. Looked ultra cool across the room- remotely stopping at each input and a matching motor driven volume too.

All of those systems are unreliable. In the case of the Yamaha motor driven input selector, made by our friends at Alps, it is half a day's work to repair the intermittent contacts issue and in most cases the entire amplifier/receiver is written off. They used those devices over many years on top models.

Simple is best. A high quality, replaceable 270 degree pot will ensure many years of reliable operation. All the other 'solutions', not so much.
 
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John, I believe we're talking about different approaches. I fully agree that simpler is better. (I suggested a motorized pot only because remote, which my short quote certainly left unclear.)

But let's assume that we commit to an electronic volume circuit & also that users prefer a front-panel knob for its traditional UI. Would using a normal pot to set a DC reference combine the 2 reasonably?
 

restorer-john

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But let's assume that we commit to an electronic volume circuit & also that users prefer a front-panel knob for its traditional UI. Would using a normal pot to set a DC reference combine the 2 reasonably?
Absolutely. And it's done regularly. Some commercial products do it. I think even Accuphase used a similar approach on some preamplifiers at one point.
 

jtwrace

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Then again, he's made a small fortune selling that gear and I haven't, so what does that tell you? :)
Tom
The average audiophile is gullible and totally misinformed.
 

jtwrace

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tomchr

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You sure AI hasn't struck the audiophile community? ;)
It wouldn't surprise me one bit if many of the subjective reviews were written by some AI algorithm.

Tom
 
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About 10-12 years ago, I designed a preamp that used the PGA2320. I still have it. It works quite well. The PGA2320 is a bit noisy, but better options are available that I could use instead.
Let me guess: You forgot to include about 12 dB of following attenuation? After all, the thing can output 8.5 Vrms if you want, and the average power amp's input sensitivity is about 1...1.5 Vrms - not a good match and a waste of dynamic range. 10 µV of noise + 29 dB is about 270 µV of output noise, that's about NJM4558 @ 16.5 dB + 29 dB level. Acceptable but nothing much to write home about. Cut it by 12 dB, and we're talking world-class performance. (I'd consider making it jumper-selectable @ 0, -12 dB, -20 dB to cover everything from tube amps to sensitive horn speakers on solid state.)

In the right spot, 120 dB of dynamic range is sufficient to cover anything from dead silence to ear damage. The DR provided by a low-noise preamp with volume pot actually is surprisingly high, 128 dB is not unusual (but of course, a good chunk of it generally is never being used, and you end up around 108-111 dB).

I have some 80s/90s examples that would blow your mind with volume controls, input selectors and other analog style 'modernisations'.

Sansui incorporating a microprocessor 'auto-search' system on an analogue tuner (T-7) that through a complicated worm/reduction drive and clutch would zoom the tuner pointer across the dial and stop on a station using up/down buttons.
Incidentally, not a new idea even then - SABA did something like this on a tube radio in like 1960.
Sony's TOTL TAE-80es preamplifier with a ridiculously unreliable motorised internal input selector that is another nightmare to repair.
They weren't the only ones to do that - remote-controlled Onkyos from around 1990 also had this. Those are mainly plagued by issues with the external input selector (inputs jumping), a switch + resistor ladder affair feeding an ADC. Apparently a combination of contact issues + lack of debouncing, a service bulletin describes a mod.
Yamaha motor driving their rotary input selectors via remote control, replete with a little indicator LED. Looked ultra cool across the room- remotely stopping at each input and a matching motor driven volume too.

All of those systems are unreliable. In the case of the Yamaha motor driven input selector, made by our friends at Alps, it is half a day's work to repair the intermittent contacts issue and in most cases the entire amplifier/receiver is written off. They used those devices over many years on top models.
Are those the ones with the silver-plated contacts (silver tarnishes - surprise) that they issued a gold contact replacement for a few years later (which has proven one of their most popular spares)? Like on the AX-1050? You just can't buy integrated amps like that any more - they had a 2-stage volume control using a 4-gang volume pot, like fancy 1970s-80s high-end preamps. A 145-170 W / 8 ohm amp with a residual noise level of 35 µV(A)! (And that's basically the power amps themselves...)
 
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restorer-john

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You just can't buy integrated amps like that any more - they had a 2-stage volume control using a 4-gang volume pot, like fancy 1970s-80s high-end preamps. A 145-170 W / 8 ohm amp with a residual noise level of 35 µV(A)! (And that's basically the power amps themselves...)
Yep. The good old days where the numbers were conservative and actually were state of the art.

200+200W/ch Sony TAN77es has a rated worst case residual of 35uV (A) >121dB S/N
Denon POA-1500 power amp >123dB S/N off a 150+150 watt for even lower residual.
The TOTL CX-1000 Yamaha preamplifier had a rated residual noise of 1.5uV.
All of the three power amps in the MX-xxx series offered phenomenally low residual noise levels:
135+135W @ 16uV(A)
170+170W @ 21uV
260+260W @ 21uV

To have a 260w/ch power amp, capable of over 1Kw into 1 ohm on transients with a residual noise of 21uV is amazing. I remember selling them and even when your ear was on the tweeter, you were hard pressed to hear anything at all, even with the demo room door closed and air-con turned off. I've got an MX-600 here in the room, but 16uV (A) is below what I can measure or reliably confirm.

I want to see some real residual noise only numbers approaching those numbers in modern power amplifiers. Trouble is, in 30 years, they have got a whole lot worse. Combine that with Class D and I don't think we'll see those numbers ever again.

Consider, SOTA has just been demonstrated in a 'headphone' amplifier with a rated residual of 1uV in 2018 (the reviewed on ASR neurochrome). And that's just a watt or so. I have 1970s preamplifiers that can swing 40V+ with source impedances so low you can drive headphones or even a speaker easily with responses ruler flat out to >300KHz. (Kenwood LO7C/2).
 
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tomchr

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Let me guess: You forgot to include about 12 dB of following attenuation?
Let me guess: You forgot to perform the noise analysis? Following an amplifier with an attenuator degrades the SNR by the attenuation of the attenuator. Not my cup of tea. Besides, the attenuator would have to be rather low impedance (few kΩ at most). Considering the PGA2320 is spec'ed at 100 kΩ load, I doubt it would be able to drive such an attenuator without degrading either a) the noise floor or b) the THD.

Tom
 

tomchr

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tomchr

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If I recall correctly a standard calibration is $1500 (US) + shipping ($350). I originally bought the APx525 without the digital I/O. I decided I needed it, so I had AP add it in to the tune of $2500 or so. Because the addition of the digital I/O was more than some dollar amount it came with a "free" calibration.

The process is pretty easy. You ship the box to the AP rep and they ship it to AP and deal with customs. You have a hole in your lab (and heart) for two weeks. Then a box shows on your doorstep and life can continue. :)

Tom
 

restorer-john

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If I recall correctly a standard calibration is $1500 (US) + shipping ($350). I originally bought the APx525 without the digital I/O. I decided I needed it, so I had AP add it in to the tune of $2500 or so. Because the addition of the digital I/O was more than some dollar amount it came with a "free" calibration.
And Amir was complaining about the prices Apple charge for apps...

:)
 

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